Hi,
I am sorry to hear about your sister-in-law's condition. Stage 4 is usually when not much can be done, except for making the patient as comfortable as possible.
Talk to the doctors regularly and see that she gets adequate pain relief.
Be there with her, so that she can treasure these moments.
You will have to be emotionally very strong.
Good luck.
I'm sorry to hear of your sister's present condition. Thought her status sounds very serious there is always hope. May I suggest you visit the following website (bcsupport.org) where you will find many Stage 4 survivors who describe their experiences. This may be of some confort to both you and your sister.